The invention relates to a method for generating welding pressure in a welding machine with electrode rollers. The invention also relates to an apparatus for this purpose.
In welding machines with electrode rollers, in which the actual electrode may be in the form of a wire electrode running over the rollers, it sometimes happens that there is insufficient fusion at the initial weld point of a workpiece with a butted or overlapped seam, in particular a can body, which is pushed between the rollers. This problem is particularly apt to occur at the high rates of travel which can now be attained. The inertia of the welding rollers, and particularly, in the case of can body welding, that of the larger outer roller, initially causes welding pressure to be excessive so that the electrical resistance of the overlapped seam is very low, which may result in a lack of fusion. Moreover this may result in microleaks in the cans fabricated by this process (aerosol cans in particular), even when the initial weld point of such cans lies in the bead region. The welding pressure must, however, reach a sufficiently high value for the remaining regions of the seam to ensure reliable transport through the welding zone and to avoid excessive vibration of the welding rollers following insertion of the workpiece between the rollers.
The basic object of the invention, therefore, is to eliminate or at least reduce the problem at the initial weld point, while ensuring that welding is performed correctly along the seam.